JP2015187290A - Ferritic stainless steel sheet for flange, method for producing the same, and flange component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferritic stainless steel sheet having a sheet thickness of 5 mm or more, while preventing the cracks upon steel sheet production, and further, to provide a flange component excellent in toughness.SOLUTION: There is provided a ferritic stainless steel made of a steel comprising, by mass, 0.001 to 0.08% C, 0.01 to 1.0% Si, 0.01 to 1.0% Mn, 0.01 to 0.05% P, 0.0002 to 0.01% S, 10.0 to 20.0% Cr and 0.001 to 0.05% N, and the balance Fe with inevitable impurities, and having a sheet thickness of 5 mm or higher, where the ratio of the area ratio of crystal grains in which the <011> direction lies within 15° to the rolling direction is 20% or higher.

Description

  The present invention is a ferritic stainless steel sheet having a thickness of 5 mm or more, which prevents cracking during the production of the steel sheet and provides a material excellent in corrosion resistance and toughness for the flange parts used in the present invention. is there.

  The exhaust gas path of an automobile includes various parts such as an exhaust manifold, a muffler, a catalyst, a flexible tube, a center pipe, and a front pipe. When connecting these parts, a fastening part called a flange is often used. In automobile exhaust system parts, flange joints are actively employed because the number of processing steps is reduced and the working space is reduced. Further, from the viewpoint of ensuring noise and rigidity due to vibration, a thick flange of 5 mm or more is often used. The flange is manufactured by stamping or other processes such as stamping. Conventionally, a normal steel plate has been used as a material. However, since ordinary steel is inferior in corrosion resistance, rust called initial rust is generated after automobile production, which may impair the appearance. For this reason, the use of a stainless steel plate as a flange material is being actively promoted instead of a plain steel plate.

  Since ferritic stainless steel sheets have a lower Ni content and are lower in cost than austenitic stainless steel sheets, ferritic stainless steel sheets are often mainly applied to flanges, but the problem is that they are inferior in toughness. If the toughness is low, there is a problem that the plate breaks during line passing and coil unfolding in the steel plate manufacturing process. In flange processing, cracks may occur during processing such as cutting and punching. Furthermore, when an impact is applied in a low-temperature environment in winter, there is a problem that the flange breaks and the automobile exhaust pipe is damaged. A thick ferritic stainless steel sheet of 5 mm or more may have particularly low toughness, and there is a problem that reliability is low when applied to a flange.

  The present invention relates to the toughness of a thick ferritic stainless steel sheet for flanges. It relates to one product. Several ideas have been made to solve the problems related to the toughness of ferritic stainless steel sheets. For example, Patent Documents 1 and 2 disclose manufacturing conditions for mass-producing ferritic stainless steel hot-rolled coils or hot-rolled annealed coils having a plate thickness of 5 to 12 mm. Patent Document 1 is directed to a Ti-containing ferritic stainless steel, and shows a method in which a coiling temperature is set to 570 ° C. or higher and a coil is immersed in water in order to adjust the hardness and Charpy impact value. On the other hand, Patent Document 2 is directed to Nb-containing ferritic stainless steel, and in order to adjust the hardness and Charpy impact value, the hot rolling finish temperature is set to 890 ° C. or higher and wound at 400 ° C. or lower, and the coil is immersed in water. How to do is shown. These specify hot rolling conditions from the viewpoint of improving the toughness of hot-rolled sheets or hot-rolled / annealed sheets, but it is difficult to control the overall coil length to the above conditions, and the metal structure for improving toughness Dominating factors were unclear. Patent Document 3 discloses a ferritic stainless steel excellent in cold cracking property in which the length of a sub-grain boundary having a small crystal orientation difference of a ferrite phase is set to a certain value or more. This is obtained by a method in which the hot rolling finishing temperature is 800 to 1000 ° C., the winding temperature is more than 650 ° C. to 800 ° C., and it is immersed in a water tank after winding. Patent Document 4 discloses a ferritic stainless steel sheet having excellent toughness that defines the proportion of grain boundary precipitates. These have been improved in toughness by controlling grain boundary characteristics and precipitates on the grain boundaries, but have not necessarily reached a satisfactory toughness level for flange applications. As this factor, it is necessary to control toughness controlling factors other than those described above, and in the present invention, earnest research has been promoted on this point.

JP 2012-140687 A JP 2012-140688 A WO2013 / 085005 JP 2009-263714 A

  An object of the present invention is to solve the problems of the known techniques and efficiently produce a ferritic stainless steel sheet for flanges having excellent toughness.

  In order to solve the above problems, the present inventors have conducted detailed studies on the low-temperature toughness of ferritic stainless steel sheets from the viewpoints of components, structure in the manufacturing process, and crystal orientation. As a result, it has been found that controlling the orientation of the parent phase crystal orientation is extremely effective for improving the toughness of hot-rolled steel sheets or hot-rolled / annealed steel sheets, especially for thick ferritic stainless steel sheets of 5 mm or more. did.

The gist of the present invention for solving the above problems is as follows.
(1) In mass%, C: 0.001 to 0.08%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, P: 0.01 to 0.05 %, S: 0.0002 to 0.01%, Cr: 10.0 to 25.0%, N: 0.001 to 0.05%, with the balance being Fe and inevitable impurities, A ferritic stainless steel for flanges having a thickness ratio of 5 mm or more and a ratio of the area ratio of crystal grains whose <011> direction is within 15 ° to the rolling direction is 20% or more.
(2) Further, in terms of mass%, Ti: 0.01 to 0.4%, Nb: 0.01 to 0.6%, B: 0.0002 to 0.0030%, Al: 0.005 to 0.00. 3%, Ni: 0.1 to 1%, Mo: 0.1 to 2.0%, Cu: 0.1 to 3.0%, V: 0.05 to 1.0%, Mg: 0.0002 -0.0030%, Sn: 0.01-0.3%, Sb: 0.01-0.3%, Zr: 0.01-0.1%, Ta: 0.01-0.1%, Hf: 0.01-0.1%, W: 0.01-2.0%, Co: 0.01-0.2%, Ca: 0.0001-0.0030%, REM: 0.001- The ferritic stainless steel for flanges according to (1), containing 0.05%, Ga: 0.0002 to 0.1%, or two or more.
(3) A hot-rolled steel sheet or a hot-rolled steel strip made of the ferritic stainless steel according to (1) or (2).
(4) A hot-rolled annealed steel plate or a hot-rolled annealed steel strip made of the ferritic stainless steel according to (1) or (2).
(5) Production of ferritic stainless steel for flanges according to (1) or (2), wherein hot rolling is performed, the hot rolling finishing temperature is 800 ° C. or higher, and the coiling temperature is 500 ° C. or lower. Method.
(6) When annealing is performed after hot rolling, annealing is performed at a heating rate of 10 ° C./sec or more to 800 to 1000 ° C., and then cooled at 10 ° C./sec or more (1) or ( 2) The manufacturing method of the ferritic stainless steel for flanges of description.
(7) The method according to (5), wherein annealing is further performed after hot rolling, and when annealing is performed, heating is performed at a heating rate of 10 ° C./sec or more to 800 to 1000 ° C. and then cooling is performed at 10 ° C./sec or more. The manufacturing method of the ferritic stainless steel for flanges of description.
(8) A hot-rolled steel plate or a hot-rolled steel strip made of ferritic stainless steel produced by the method described in (5).
(9) A hot-rolled annealed steel plate or a hot-rolled annealed steel strip made of ferritic stainless steel produced by the method according to (6) or (7).
(10) A ferritic stainless steel flange part comprising the ferritic stainless steel according to (1) or (2), wherein the ferritic stainless steel flange part is not broken by applying an impact energy of 125 J or less at −20 ° C.

  As is apparent from the above description, according to the present invention, a ferritic stainless steel sheet for flanges having excellent toughness can be efficiently provided without requiring new equipment.

It is a figure which shows the relationship between <011> azimuth | direction ratio and a Charpy impact value. It is a figure which shows a flange component. It is a figure which shows the low temperature drop test method of a flange component.

The reason for limitation of the present invention will be described below. To improve toughness, refinement of crystal grains, refinement of precipitates and softening contribute. However, it has been difficult to secure sufficient toughness for flange applications only with thick ferritic stainless steel hot-rolled sheets or hot-rolled / annealed sheets having a thickness of 5 mm or more with many additive elements. In the present invention, as a result of investigating in detail the relationship with toughness by paying attention to the crystal orientation of the ferrite phase that is the parent phase, the crystal grains in which the <011> direction, which is the stable orientation of hot rolling, is within 15 ° with respect to the rolling direction. It was found that toughness is improved by forming 20% or more (hereinafter also referred to as “<011> oriented grains”) in terms of area ratio. FIG. 1 shows <011 of hot-rolled sheets or hot-rolled / annealed sheets of steels (17% Cr-0.34% Nb-0.005% C-0.01% N) manufactured by various manufacturing methods and having different thicknesses. > The relationship between the orientation grain ratio and the Charpy impact value is shown. Here, EBSP (Electron Back-Sccetering Difraction Pattern) is used as the crystal orientation, and the orientation for each crystal grain is measured for the total thickness of the hot-rolled sheet or hot-rolled / annealed sheet, and the <011> direction is the rolling direction. The area ratio of crystal grains within the range (hereinafter also referred to as “<011> orientation ratio”) was measured. For the Charpy impact value, a V-notch test piece (provided with a V-notch in the width direction) was taken from a hot-rolled / annealed plate, and the impact value at 0 ° C. was measured according to JISZ2242. Accordingly, when the <011> orientation ratio is 20% or more, the impact value is improved and the toughness is improved. Here, good toughness means that the impact value at 0 ° C. has an impact value of 7 J / cm ² or more, and no brittle cracking occurs when the hot-rolled coil is deployed and threaded. The cleavage plane of ferritic steel is the {100} plane, and it is known that brittle cracks occur along this plane. However, when <011> oriented grains develop, the angle between the crack propagation direction and the cleavage plane increases. Therefore, it is considered that the resistance to cleavage fracture increases and the toughness value is improved.

  Next, the component range of steel will be described. % Of component content means the mass%.

  Since C deteriorates toughness by hardening by solid solution C and precipitation of carbide, the smaller the content, the better. Further, if it exceeds 0.08%, the crystal orientation is randomized due to the formation of carbides, and the development of the <011> orientation is suppressed, so the upper limit was made 0.08%. However, excessive reduction leads to an increase in refining costs, so the lower limit was made 0.001%. Furthermore, if considering the manufacturing cost, corrosion resistance, and hot rolled sheet toughness, 0.002 to 0.015% is desirable.

  Si may be added as a deoxidizing element and also improves oxidation resistance. However, since Si is a solid solution strengthening element, it is better as it is smaller in terms of toughness. Further, if it exceeds 1.0%, the development of <011> orientation is suppressed due to the change of the slip system, so the upper limit was made 1.0%. On the other hand, in order to ensure oxidation resistance, the lower limit was made 0.01%. However, excessive reduction leads to an increase in refining costs, so 0.05 to 0.9% is desirable in consideration of the material and initial rust resistance.

  Mn, like Si, is a solid solution strengthening element, so the smaller the content, the better. Further, if it exceeds 1.0%, the crystal orientation is randomized due to the formation of precipitates such as MnS and the development of <011> orientation is suppressed, so the upper limit was made 1.0%. On the other hand, excessive reduction leads to an increase in refining cost, and addition of a small amount of Mn improves scale peelability, so the lower limit was made 0.01%. Furthermore, if considering the material and manufacturing cost, 0.1 to 0.5% is desirable.

  P is a solid solution strengthening element like Mn and Si and hardens the material. Therefore, the smaller the content, the better from the viewpoint of toughness. Further, if it exceeds 0.05%, randomization of crystal orientation occurs due to the formation of phosphide, and the development of <011> orientation is suppressed, so the upper limit was made 0.05%. However, excessive reduction leads to an increase in raw material cost, so the lower limit was made 0.01%. Furthermore, if considering the manufacturing cost and corrosion resistance, 0.015 to 0.03% is desirable.

Since S is an element that degrades corrosion resistance, the smaller the content, the better. On the other hand, if it exceeds 0.01%, the crystal orientation is randomized due to the formation of precipitates such as MnS and Ti ₄ C ₂ S ₂ , and the development of the <011> orientation is suppressed. 0.01%. On the other hand, there is an effect of improving punchability in flange molding by combining with Mn and Ti, and since this is manifested from 0.0002%, the lower limit was made 0.0002%. Furthermore, when considering refining costs and suppression of crevice corrosion when fuel parts are used, 0.0010 to 0.0060% is desirable.

  Cr is an element that improves the corrosion resistance and oxidation resistance, and considering the salt damage required for the flange, 10.0% or more is necessary. On the other hand, excessive addition becomes hard and deteriorates moldability and toughness. If it exceeds 25.0%, the crystal orientation is randomized due to the formation of precipitates such as coarse Cr carbide and nitride, and the development of the <011> orientation is suppressed. 0%. In addition, if considering the plate cost at the time of manufacturing due to the manufacturing cost and toughness deterioration, 10.0 to 18.0% is desirable.

  N, like C, deteriorates toughness and corrosion resistance, so the smaller the content, the better. If it exceeds 0.05%, the crystal orientation is randomized due to the formation of nitrides, and the development of the <011> orientation is suppressed, so the upper limit was made 0.05%. However, excessive reduction leads to an increase in refining costs, so the lower limit was made 0.001%. Furthermore, if considering the manufacturing cost, workability, and initial rustability, 0.005 to 0.02% is desirable.

  Furthermore, the present invention preferably contains the following elements selectively.

  Ti is an element that is added as necessary to combine with C, N, and S to improve corrosion resistance, intergranular corrosion resistance, and toughness. Since the C and N fixing action starts from 0.01%, the lower limit was made 0.01%. Further, addition of more than 0.4% hardens, coarse Ti (C, N) precipitates and remarkably deteriorates toughness, and suppresses the development of <011> orientation. %. Furthermore, if considering the manufacturing cost, 0.05 to 0.25% is desirable.

Nb is added as needed in order to improve the high temperature strength and to combine with C and N like Ti to improve corrosion resistance, intergranular corrosion resistance, and toughness. Since this effect appears at 0.01% or more, the lower limit was made 0.01%. However, excessive addition hardens and deteriorates formability, and depending on coarse Nb (C, N) and thermal history, (Fe, Nb) ₆ C and Fe ₂ Nb precipitate and remarkably deteriorate toughness. In order to suppress the development of the <011> orientation, the upper limit was made 0.6%. In consideration of raw material costs and crevice corrosion, 0.1 to 0.45% is desirable.

  B is an element that improves the secondary workability of the product by segregating at the grain boundaries, and is added as necessary to improve the punchability of the flange. Since this effect appears at 0.0002% or more, the lower limit was made 0.0002%. However, excessive addition causes precipitation of borides to deteriorate toughness and suppresses the development of the <011> orientation, so the upper limit was made 0.0030%. Furthermore, if considering cost and ductility reduction, 0.0003 to 0.0010% is desirable.

  In some cases, Al is added as a deoxidizing element, and its action is manifested from 0.005%, so the lower limit was made 0.005%. Further, addition of 0.3% or more brings about a decrease in toughness, deterioration of weldability and surface quality, and suppresses the development of <011> orientation, so the upper limit was made 0.3%. Furthermore, if considering the refining cost, 0.01 to 0.1% is desirable.

  Ni is added as needed to improve the initial rust resistance by suppressing crevice corrosion and promoting repassivation. Since this effect appears at 0.1% or more, the lower limit was made 0.1%. However, excessive addition hardens and deteriorates moldability, suppresses the development of the <011> orientation, and easily causes stress corrosion cracking, so the upper limit was made 1%. In consideration of the raw material cost, 0.1 to 0.5% is desirable.

  Mo is an element that improves corrosion resistance and high-temperature strength, and is an element that is necessary to suppress crevice corrosion, particularly when it has a crevice structure. Since this effect appears from 0.1%, the lower limit was made 0.1%. On the other hand, if it exceeds 2.0%, the formability is remarkably deteriorated, the toughness is deteriorated during production, and the development of the <011> orientation is suppressed, so the upper limit was made 2.0%. Furthermore, if considering the manufacturing cost, 0.1 to 1.2% is desirable.

  Cu is added as necessary in order to enhance crevice corrosion and promote repassivation in addition to improving high-temperature strength. Since this effect appears from 0.1% or more, the lower limit was made 0.1%. However, excessive addition hardens by ε-Cu precipitation and deteriorates formability and toughness, and also suppresses the development of the <011> orientation, so the upper limit was made 3.0%. In view of pickling properties at the time of manufacture, 0.1 to 1.2% is desirable.

  V suppresses crevice corrosion and contributes to toughness improvement by addition of a small amount, and is added as necessary. Since this effect appears from 0.05% or more, the lower limit was made 0.05%. However, excessive addition hardens and deteriorates moldability, and coarse V (C, N) leads to toughness deterioration and suppression of <011> orientation due to precipitation, so the upper limit was made 1.0%. In consideration of the raw material cost and initial rusting property, 0.07 to 0.2% is desirable.

  Mg may be added as a deoxidizing element, and is an element that contributes to improving the formability by refining the slab structure. Further, the Mg oxide becomes a precipitation site for carbonitrides such as Ti (C, N) and Nb (C, N), and has an effect of finely dispersing and depositing them. This effect appears at 0.0002% or more, and contributes to toughness improvement, so the lower limit was made 0.0002%. However, excessive addition leads to deterioration of weldability and corrosion resistance, and also leads to suppression of <011> orientation due to coarse precipitate formation, so the upper limit was made 0.0030%. Considering the refining cost, 0.0003 to 0.0010% is desirable.

  Sn and Sb are added in an amount of 0.01% or more as necessary to contribute to improvement of corrosion resistance and high temperature strength. In addition to the addition of more than 0.3%, slab cracking may occur during the manufacture of the steel sheet, and the upper limit is set to 0.3% to suppress the development of the <011> orientation. Furthermore, if considering refining costs and manufacturability, 0.01 to 0.15% is desirable.

  Zr, Ta, and Hf are combined with C and N to contribute to improvement of toughness, and if necessary, 0.01% or more is added. However, the addition of more than 0.1% increases the cost and significantly degrades the productivity and suppresses the development of the <011> orientation, so the upper limit is made 0.1%. Furthermore, if considering refining costs and manufacturability, 0.01 to 0.08% is desirable.

  W contributes to the improvement of corrosion resistance and high temperature strength, so 0.01% or more is added as necessary. Addition of more than 2.0% leads to toughness deterioration during steel plate production, suppression of <011> orientation and cost increase, so the upper limit is set to 2.0%. Furthermore, if refining costs and manufacturability are taken into consideration, 0.01 to 1.0% is desirable.

  Co contributes to improving the high-temperature strength, so 0.01% or more is added as necessary. Addition of over 0.2% leads to toughness deterioration during steel plate production, suppression of <011> orientation, and cost increase, so the upper limit is set to 0.2%. Furthermore, if refining costs and manufacturability are taken into consideration, 0.01 to 0.1% is desirable.

  Ca may be added for desulfurization, and this effect is manifested at 0.0001% or more, so the lower limit was made 0.0001%. However, addition of over 0.0030% produces coarse CaS, which deteriorates toughness and corrosion resistance and suppresses the <011> orientation, so the upper limit was made 0.0030%. Furthermore, if considering refining costs and manufacturability, 0.0003 to 0.0020% is desirable.

  REM may be added as necessary from the viewpoint of improving toughness and oxidation resistance by refining various precipitates, and since this effect is manifested at 0.001% or more, the lower limit is set to 0.00. 001%. However, addition of more than 0.05% significantly deteriorates castability and suppresses the development of the <011> orientation, so the upper limit was made 0.05%. Furthermore, if considering the refining cost and manufacturability, 0.001 to 0.01% is desirable. REM (rare earth element) refers to a generic name of two elements of scandium (Sc) and yttrium (Y) and 15 elements (lanthanoid) from lanthanum (La) to lutetium (Lu) according to a general definition. It may be added alone or as a mixture.

  Ga may be added at 0.1% or less for improving corrosion resistance and suppressing hydrogen embrittlement. The lower limit is made 0.0002% from the viewpoint of sulfide and hydride formation. Preferably it is 0.0010% or more. Furthermore, 0.0040% or less is preferable from the viewpoint of manufacturability and cost, and from the viewpoint of <011> orientation development.

  Although it does not prescribe | regulate especially in this invention about another component, in this invention, you may add 0.001 to 0.1% of Bi etc. as needed. Note that it is preferable to reduce general harmful elements and impurity elements such as As and Pb as much as possible.

  Next, a manufacturing method will be described. The steel sheet of the present invention is produced by the steps of steelmaking-hot rolling, steelmaking-hot rolling-pickling or steelmaking-hot rolling-annealing-pickling. In steelmaking, a method in which the steel containing the above essential components and components added as necessary is subjected to furnace melting followed by secondary refining. The molten steel is made into a slab according to a known casting method (continuous casting). The slab is heated to a predetermined temperature and hot-rolled to a predetermined plate thickness by continuous rolling.

  In the present invention, a finishing temperature and a winding temperature in hot rolling are defined. As the finishing temperature increases, the processing strain of the ferrite phase is removed and the structure recovery is accelerated after finishing rolling, and the formation of subgrains having <011> orientation grains (crystal grains whose <011> direction is within 15 ° with respect to the rolling direction). Contributes to improved toughness. In addition, when the finishing temperature is less than 800 ° C., orientations other than the <011> orientation grains (<001> orientation, etc.) are generated and developed due to hot-rolled shear strain. By setting the finishing temperature to 800 ° C. or higher, the other position is suppressed, and <011> oriented grains having a subgrain structure are obtained in an amount of 20% or more. Therefore, the finishing temperature is set to 800 ° C. or higher. However, an excessively high temperature suppresses the formation of <011> oriented grains and leads to a decrease in pickling properties, so the upper limit of the finishing temperature is set to 900 ° C. Furthermore, considering the surface defects, 810 to 880 ° C. is desirable.

  Although the winding process is performed after finish rolling, the upper limit of the coiling temperature is set to 500 ° C. in order to reduce the toughness due to the formation of precipitates that cause toughness reduction at high temperature coiling exceeding 500 ° C. and 475 ° brittleness. Further, in order to suppress the crystal orientation rotation of <011> oriented grains having a subgrain structure formed during finish rolling performed at a finish temperature of 800 ° C. or higher, and not to have a recrystallized structure, a coiling upper limit temperature of 500 ℃ is required. However, excessively low temperature results in a defective coil shape, so the lower limit is set to 200 ° C. Furthermore, if the shape stability and pickling properties are taken into consideration, the coiling temperature is preferably 300 to 450 ° C. The hot-rolled sheet thickness is 5 mm or more, which is frequently used as a flange. However, if the thickness is excessively increased, the toughness is extremely lowered, so that the thickness is desirably 5 to 20 mm.

  An annealing condition is prescribed | regulated, when passing an annealing-pickling process after hot rolling. As the annealing temperature is raised, recovery and recrystallization proceed, and <011> oriented grains are reduced. In order to suppress this, it heats to 800-1000 degreeC. If the heating temperature is less than 800 ° C., the work structure at the hot rolling stage remains and the recovery does not proceed sufficiently and is hard, so that the toughness becomes poor. Further, when the heating temperature exceeds 1000 ° C., the grain growth after completion of recrystallization progresses remarkably, and the randomization of the crystal orientation progresses and the <011> orientation grains are reduced, so that the toughness is remarkably deteriorated. When heating, the heating rate is set to 10 ° C./sec or more. When the heating rate is slower than this, recrystallization proceeds to cause the disappearance of the subgrain structure and the coarsening of the crystal grains, and the <011> orientation grains are reduced and the toughness is deteriorated. The reason why the <011> oriented grains are reduced at a heating rate of less than 10 ° C./sec is that the other position is generated during the slow heating and the <011> oriented grains are phagocytosed. In particular, the <112> and <100> orientations develop and it is difficult for the <011> orientation grain content ratio to satisfy 20%. Also, the cooling rate is 10 ° C./sec or more, but this is to suppress the formation of precipitates that cause toughness deterioration during the cooling process. On the other hand, when the cooling rate is less than 10 ° C./sec, the crystal orientation changes in the cooling process and the <011> orientation ratio decreases. Furthermore, in consideration of productivity, it is desirable that the heating rate is 15 ° C./sec or more and the cooling rate is 15 ° C./sec or more. In addition, if it is a component composition of this invention, an effect will fully be expressed with said cooling rate. Even if the cooling rate is higher than the above (for example, 50 ° C./sec or more), the effect of the present invention is saturated. In the present invention, it is preferable that the cooling rate is less than 50 ° C./sec in consideration of the surface quality, the shape of the steel plate and the manufacturing cost. Further, the heating temperature is preferably 850 to 950 ° C. from the viewpoints of solid solution of precipitates, suppression of crystal grain coarsening, and residual <011> orientation.

  The ferritic stainless steel of the present invention that has undergone hot rolling constitutes a hot-rolled steel sheet or a hot-rolled steel strip. The ferritic stainless steel of the present invention that has been annealed after hot rolling constitutes a hot rolled annealed steel sheet or a hot rolled annealed steel strip.

  Steel having the component composition shown in Table 1 was melted and cast into a slab, and the slab was hot-rolled to a thickness of 5 mm or more to obtain a hot-rolled coil. At this time, the hot rolling finishing temperature was controlled to 810 to 880 ° C, and the winding temperature was controlled to 300 to 450 ° C. Thereafter, a coil to be annealed was also manufactured. The annealing temperature at this time was 850 to 950 ° C., and the heating rate and the cooling rate were both 15 ° C./sec. Crystal orientation evaluation samples and Charpy impact test pieces were collected from these hot-rolled sheets or hot-rolled / annealed sheets. EBSP is used as the crystal orientation, and the orientation of each crystal grain is measured for the total thickness of the hot-rolled sheet or hot-rolled / annealed sheet, and the <011> direction is within 15 ° with respect to the rolling direction (< 011> azimuth ratio) (area%) was measured. The Charpy impact test was carried out by the above method according to JISZ2242.

Table 1 shows the results. Invention Examples A1 to A20 had the components of the present invention, the <011> orientation ratio was 20% or more, and the impact value at 0 ° C. was 7 J / cm ² or more. In Comparative Examples B1 to B26, any component was outside the scope of the present invention, the <011> orientation ratio was less than 20%, and the impact value at 0 ° C. did not reach 7 J / cm ² in many cases. If the impact value at 0 ° C. is a steel having an impact value of 7 J / cm ² or more, brittle cracks do not occur when the hot-rolled coil is deployed and passed, but the steel and manufacturing method of the present invention are sufficient. It turns out that it has toughness.

The evaluation result of the coil which changed hot rolling conditions and annealing conditions as shown in Table 2 with respect to the steel which has the component of this invention is shown. Steel No. in Table 2 No. in Table 1 And the corresponding No. The production method described in Table 2 is applied. Inventive examples C1 to C24 in Table 2 apply the production conditions of the present invention, and good toughness is obtained. On the other hand, in Comparative Examples D1 to D6, any of the production conditions was outside the scope of the present invention, the <011> orientation ratio was less than 20%, and the impact value at 0 ° C. did not reach 7 J / cm ² .

  Table 2 shows the results of a low-temperature drop test after flange processing using a hot-rolled sheet or a hot-rolled / annealed sheet as a raw material. FIG. 2 shows an example of the flange component 1. FIG. 3 shows the method of the low temperature drop test. Using a drop weight test apparatus 2, a weight 3 having a weight of 16 kg was freely dropped from a height of 80 cm onto the side surface of the flange part 1 cooled to −20 ° C., and the presence or absence of cracking of the flange part 1 was visually observed. In this case, the energy applied to the flange part is 125J. The method of cooling the flange parts to −20 ° C. was performed by adjusting the temperature with a constant temperature / humidity bath or alcohol and liquid nitrogen, holding at −20 ° C. for 10 minutes, and then applying an impact. From Table 2, it is possible to provide a flange part that is excellent in low temperature toughness without being cracked by application of impact energy of −125 ° C. or lower at −20 ° C.

  Note that other conditions in the manufacturing process may be appropriately selected. For example, what is necessary is just to design slab thickness, hot rolling board thickness, etc. suitably. It may be immersed in a water-cooled pool after hot rolling. For pickling after hot rolling or after hot rolling annealing, mechanical descaling methods such as shot blasting, bending, and brush may be selected as appropriate, and the existing conditions such as sulfuric acid and nitric hydrofluoric acid may be used for the acid solution. Further, after this, coil grinding may be applied to the surface.

  As is clear from the above description, the stainless hot-rolled steel sheet according to the present invention is excellent in manufacturability and toughness during flange production and use. That is, by using the material to which the present invention is applied, particularly as an automobile or a motorcycle part, it is possible to ensure reliability and increase the social contribution, which is extremely useful industrially.

1 Flange parts 2 Drop weight test device 3 Weight

The gist of the present invention for solving the above problems is as follows.
(1) In mass%, C: 0.001 to 0.08%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, P: 0.01 to 0.05 %, S: 0.0002 to 0.01%, Cr: 10.0 to 25.0%, N: 0.001 to 0.05%, with the balance being Fe and inevitable impurities, A hot-rolled steel sheet or hot-rolled steel made of ferritic stainless steel for flanges, wherein the ratio of the area ratio of crystal grains having a thickness of 5 mm or more and the <011> direction within 15 ° with respect to the rolling direction is 20% or more Steel strip .
(2) Further, in terms of mass%, Ti: 0.01 to 0.4%, Nb: 0.01 to 0.6%, B: 0.0002 to 0.0030%, Al: 0.005 to 0.00. 3%, Ni: 0.1 to 1%, Mo: 0.1 to 2.0%, Cu: 0.1 to 3.0%, V: 0.05 to 1.0%, Mg: 0.0002 -0.0030%, Sn: 0.01-0.3%, Sb: 0.01-0.3%, Zr: 0.01-0.1%, Ta: 0.01-0.1%, Hf: 0.01-0.1%, W: 0.01-2.0%, Co: 0.01-0.2%, Ca: 0.0001-0.0030%, REM: 0.001- 0.05%, Ga: 0.0002 to 0.1%, or one or more, containing Mn content of 0.01 to 0.5% Ferrite stainless steel for flange Hot-rolled steel sheet or hot rolled strip of steel.
( 3 ) In mass%, C: 0.001 to 0.08%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, P: 0.01 to 0.05 %, S: 0.0002 to 0.01%, Cr: 10.0 to 25.0%, N: 0.001 to 0.05%, with the balance being Fe and inevitable impurities, A hot-rolled annealed steel plate or a heat-treated steel sheet made of ferritic stainless steel for flanges, characterized in that the ratio of the area ratio of crystal grains having a thickness of 5 mm or more and the <011> direction within 15 ° with respect to the rolling direction is 20% or more Annealed steel strip .
( 4 ) Further, in terms of mass%, Ti: 0.01 to 0.4%, Nb: 0.01 to 0.6%, B: 0.0002 to 0.0030%, Al: 0.005 to 0.00. 3%, Ni: 0.1 to 1%, Mo: 0.1 to 2.0%, Cu: 0.1 to 3.0%, V: 0.05 to 1.0%, Mg: 0.0002 -0.0030%, Sn: 0.01-0.3%, Sb: 0.01-0.3%, Zr: 0.01-0.1%, Ta: 0.01-0.1%, Hf: 0.01-0.1%, W: 0.01-2.0%, Co: 0.01-0.2%, Ca: 0.0001-0.0030%, REM: 0.001- The hot-rolled annealed steel sheet or hot-rolled steel made of ferritic stainless steel for flanges according to ( 3 ), containing 0.05%, Ga: 0.0002 to 0.1%, or one or more of them Annealed steel strip .
(5) subjected to hot rolling, hot-rolled finishing temperature of 800 ° C. or higher, consisting of coiling temperature, characterized in that a 500 ° C. or less (1) or (2) flange ferritic stainless steel according A method for producing a hot-rolled steel sheet or a hot-rolled steel strip .
(6) subjected to hot rolling, hot-rolled finishing temperature of 800 ° C. or higher, consisting of coiling temperature, characterized in that a 500 ° C. or less (3) or (4) flange ferritic stainless steel according A method for producing a hot-rolled annealed steel sheet or a hot-rolled annealed steel strip .
( 7 ) When annealing, the ferrite system for flange according to ( 3 ) or ( 4 ), characterized in that after heating to 800-1000 ° C at a heating rate of 10 ° C / sec or more, cooling is performed at 10 ° C / sec or more. A method for producing a hot-rolled annealed steel strip or a hot-rolled annealed steel strip made of stainless steel.
(8) when annealing from 10 ° C. / after heating sec or more heating speeds 800 to 1000 ° C., 10 ° C. /, characterized in that sec cooling above (6) flange ferritic stainless steel according to A method for producing a hot-rolled annealed steel sheet or a hot-rolled annealed steel strip .
( 9 ) A flange part made of a hot-rolled steel sheet or a hot-rolled steel strip made of ferritic stainless steel as described in (1) or (2), and not broken by applying an impact energy of ≦ 125 J at −20 ° C. Featuring ferritic stainless steel flange parts.
(10) A flange part made of a hot-rolled annealed steel plate or a hot-rolled annealed steel strip made of a ferritic stainless steel according to ( 3 ) or ( 4 ), and does not break when applied with an impact energy of 125 J or less at −20 ° C. Ferritic stainless steel flange parts characterized by this.

Claims (10)

  In mass%, C: 0.001 to 0.08%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, P: 0.01 to 0.05%, S : 0.0002 to 0.01%, Cr: 10.0 to 25.0%, N: 0.001 to 0.05%, with the balance being Fe and inevitable impurities, with a plate thickness of 5 mm As described above, the ferritic stainless steel for flanges, wherein the ratio of the area ratio of crystal grains whose <011> direction is within 15 ° with respect to the rolling direction is 20% or more.   Furthermore, in mass%, Ti: 0.01-0.4%, Nb: 0.01-0.6%, B: 0.0002-0.0030%, Al: 0.005-0.3%, Ni: 0.1-1%, Mo: 0.1-2.0%, Cu: 0.1-3.0%, V: 0.05-1.0%, Mg: 0.0002-0. 0030%, Sn: 0.01 to 0.3%, Sb: 0.01 to 0.3%, Zr: 0.01 to 0.1%, Ta: 0.01 to 0.1%, Hf: 0 0.01-0.1%, W: 0.01-2.0%, Co: 0.01-0.2%, Ca: 0.0001-0.0030%, REM: 0.001-0.05 %, Ga: 0.0002 to 0.1%, or two or more of ferritic stainless steels for flanges according to claim 1.   A hot-rolled steel plate or a hot-rolled steel strip made of the ferritic stainless steel according to claim 1.   A hot-rolled annealed steel sheet or a hot-rolled annealed steel strip made of the ferritic stainless steel according to claim 1 or 2.   The method for producing a ferritic stainless steel for flange according to claim 1 or 2, wherein hot rolling is performed, the hot rolling finishing temperature is set to 800 ° C or higher, and the winding temperature is set to 500 ° C or lower.   3. The method according to claim 1, wherein when annealing is performed after hot rolling, the steel is heated to 800 to 1000 ° C. at a heating rate of 10 ° C./sec or more and then cooled at 10 ° C./sec or more. Manufacturing method of ferritic stainless steel for flanges.   6. The flange according to claim 5, further comprising annealing after hot rolling and heating to 800 to 1000 ° C. at a heating rate of 10 ° C./sec or more and then cooling at 10 ° C./sec or more. For producing ferritic stainless steels for use in steel.   A hot-rolled steel sheet or a hot-rolled steel strip made of ferritic stainless steel produced by the method according to claim 5.   A hot-rolled annealed steel sheet or a hot-rolled annealed steel strip made of ferritic stainless steel produced by the method according to claim 6 or 7.   A ferritic stainless steel flange part comprising the ferritic stainless steel according to claim 1 or 2, which is not broken by applying an impact energy of 125 J or less at -20 ° C.

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